1. Technical Field
The invention relates to a wafer boat comprising an end member on both extremities connected by at least three axial rods, which rods define a housing surface for receiving of a number of axially spaced wafers. Moreover, for each wafer there are at least three supporting means connected to those columns and provided with accommodations.
2. Background Art
Such wafer boats are usually used vertically, that is, the wafers lie horizontally, one above the other. Any number of wafers can be accepted in such a boat. Such a boat is placed in a reactor where the wafer undergoes a treatment. Many types of treatment are possible, such as heat treatment, oxidation and other chemical and/or physical reactions.
With that, the problem of non-uniformity across the wafer surface occurs. That is, if the treatment gas is supplied radially, this will be depleted towards the center of the wafer. Consequently, the process or reaction in question will be further advanced at the edge of the wafer than in the center of the wafer. Such a non-uniformity is particularly undesirable.
In the American patent U.S. Pat. No. 5,192,371 in the name of ASM Japan K.K., the use of rings is described which are fitted at some distance under the wafer. The internal diameter of the ring corresponds to, or is a little smaller than, the external diameter of the wafer. Consequently, the uniformity of the reaction across the wafer surface is considerably increased, since the edge effect then occurs in the relevant ring.
A further embodiment of such a ring is encountered in the American patent U.S. Pat. No. 5,316,472.
In the first mentioned American patent U.S. Pat. No. 5,192,371, the ring also provides the supporting surface for the wafer.